Using High-Energy Neutrinos As Cosmic Magnetometers

TL;DR

This paper investigates how high-energy neutrinos can be used to measure magnetic fields in their astrophysical sources by analyzing IceCube data for signs of synchrotron energy losses.

Contribution

It introduces a novel method of using neutrino energy and flavor data as cosmic magnetometers to constrain magnetic field strengths in neutrino sources.

Findings

No evidence of synchrotron losses found in IceCube data.

Upper limit of 10 kG-10 MG on source magnetic fields at 95% confidence.

Method provides new constraints on the magnetic environment of neutrino sources.

Abstract

Magnetic fields are crucial in shaping the non-thermal emission of the TeV-PeV neutrinos of astrophysical origin seen by the IceCube neutrino telescope. The sources of these neutrinos are unknown, but if they harbor a strong magnetic field, then the synchrotron energy losses of the neutrino parent particles---protons, pions, and muons---leave characteristic imprints on the neutrino energy distribution and its flavor composition. We use high-energy neutrinos as "cosmic magnetometers" to constrain the identity of their sources by placing limits on the strength of the magnetic field in them. We look for evidence of synchrotron losses in public IceCube data: 6 years of High Energy Starting Events (HESE) and 2 years of Medium Energy Starting Events (MESE). In the absence of evidence, we place an upper limit of 10 kG-10 MG (95% C.L.) on the average magnetic field strength of the sources.